Chun Huh

Nanoparticle-stabilized carbon dioxide-in-water foams with fine texture

The concept of hydrophilic/CO(2)-philic balance (HCB) was extended to describe stabilization of carbon dioxide-in-water (C/W) foams (also called emulsions) with silica nanoparticles adsorbed at the CO(2)-water interface. Opaque, white C/W foams (bubble diameter <100 μm) were generated with either PEG-coated silica or methylsilyl modified silica nanoparticles in a beadpack with CO(2) densities between 0.2 and 0.9 g mL(-1). For methylsilyl modified silica nanoparticles, 50% SiOH modification provided an optimal HCB for generation and stabilization of viscous C/W foams with high stability. The apparent viscosity measured with a capillary tube viscometer reached 120-fold that of a CO(2)-water mixture without nanoparticles, a consequence of the small bubble size and the energy required to deform a high density of aqueous lamellae between CO(2) bubbles. Air-in-water (A/W) foams stabilized with nanoparticles were used to gain insight into the relationship between nanoparticle surface properties and adsorption of the nanoparticles at various types of interfaces. With suitable nanoparticles, A/W foams were stable for at least 7 days and C/W foams were stable for at least 23 h. The ability to achieve long term stability for nanoparticle stabilized C/W foams could offer an alternative to conventional surfactants, which are known to have much lower adsorption energies.

Nanoparticle-Stabilized Emulsions for Applications in Enhanced Oil Recovery

Nanoparticle-stabilized emulsions have attracted many researchers’ attention in recent years due to many of their specific characteristics and advantages over conventional emulsions stabilized by surfactants or by colloidal particles. For example, the solid nanoparticles can be irreversibly attached to the oil-water interface and form a rigid nanoparticle monolayer on the droplet surfaces, which induce highly stable emulsions. Those emulsions can withstand harsh conditions. Compared to colloidal particles, nanoparticles are one hundred times smaller, and emulsions stabilized by them can travel a long distance in reservoirs without much retention. Oil-in-water and water-in-oil emulsions that are stabilized with different surface-coated silica nanoparticles of uniform size have been developed; these emulsions remain stable for several months without coalescence. The wettability of the nanoparticle determines the type of emulsion formed. The phase behavior with respect to the initial water/oil volume ratio (IVR), salinity, nanoparticle concentration and nanoparticle wettability was systematically examined. The emulsions were also characterized by measuring their droplet size and their apparent viscosity. Employing the hard-sphere liquid theory for nano-scale dispersions, the correlation between droplet/droplet interaction forces and droplet/droplet equilibrium separation distances has also been examined. Introduction Oil/water emulsions stabilized by surfactants are frequently used in the oil industry. Emulsions are also producible with solid particles as stabilizers. These are called “Pickering emulsions”. Such emulsions have many advantages over conventional surfactant-stabilized emulsions, and are widely used in food, pharmacy and cosmetics industry, but are rarely applied for oil recovery purpose. This is because the solid stabilizers they use are colloidal particles, which are in micron size and easily trapped in the rock pores. Thus the long-distance propagation of emulsions made with them is unfeasible in reservoirs. Nanoparticles have properties potentially useful for certain oil recovery processes, as they are solid and two orders of magnitude smaller than colloidal particles. The nanoparticle stabilized emulsions droplets are small enough to pass typical pores, and flow through the reservoir rock without much retention. They also remain stable despite harsh conditions in reservoirs due to the irreversible adsorption of the nanoparticles on their droplet surface. In addition, the large viscosity of nanoparticle-stabilized emulsions can help to manage the mobility ratio during flooding, which provides a viable method to push highly viscous oil from the subsurface. Therefore, they have significant potential in reservoir engineering applications. In recent years, nanoparticle-stabilized emulsions have triggered great interest. Active research efforts are on-going in many areas, especially in chemical engineering and materials science. These research efforts led to the detailed characterization of the properties of emulsions solely stabilized by nanoparticles in many aspects, e.g., emulsion type, droplet size, stability, bulk viscosity, and interfacial properties, etc. The influence of experimental conditions such as nanoparticle wettability, particle concentration, their initial location (i.e., dispersed in water or dispersed in oil), salt concentration and pH of the aqueous phase, as well as the oil type, on the emulsion system has also elucidated, and detailed reviews are available (Binks and Lumdson,2000a, 2002b; Binks et al.,2005; Binks and Rodrigues, 2005; Horozov, et al., 2007). The most commonly used nanoparticles are spherical fumed silica particles with a diameter in the range of several to tens of nanometers. Their wettability is controlled by the coating extent of silanol groups on their surface (Binks, 2002). The nanoparticles can be made hydrophilic with high percentage (over 90%) of silanol groups on the surface, and consequently they form stable oil-in-water (o/w) emulsions. On the other hand, when the silica particles are only coated about 10% on their surface by silanol groups, they are hydrophobic and yield water-in-oil (w/o) emulsions. Furthermore, when the nanoparticles

Nanoparticle-Stabilized Supercritical CO2 Foams for Potential Mobility Control Applications

The petroleum industry has been utilizing surfactant stabilized foams for mobility control and enhanced oil recovery applications. However, if surface-treated nanoparticles were utilized instead of surfactants, foams stabilized with such particles could have a number of important advantages. The solid-stabilized foams are known to have a much better stability than the surfactant-stabilized foams, because the energy required to bring nanoparticles to, and detach from the foam bubble surface is much larger than that of surfactants, and thus the resulting foam will be more stable. Since nanoparticles are the stabilizing component of the foam and are solid, they have potential to stabilize foam at high temperature conditions for extended periods of time. Since they are inherently small, nanoparticles, as well as the foam that they stabilize, can be transported through rocks without causing plugging in pore throats. Stable supercritical carbon dioxide-in-water foams were created using 5 nm silica-core nanoparticles whose surface had short polyethylene-glycol chains covalently bonded to it. The foams were made by injecting CO2 and an dispersion of with surface-treated

Superparamagnetic nanoclusters coated with oleic acid bilayers for stabilization of emulsions of water and oil at low concentration

Emulsions of water and dodecane with drop sizes down to 1 microm were stabilized with 30-100 nm interfacially active nanoclusters of sub-15 nm iron oxide primary particles at an extremely low loading of 0.14 wt.%. The nanoclusters, coated with a bilayer of oleic acid, formed stable dispersions in water at pH 7-10. The phase behavior and droplet morphologies of the emulsions of water and dodecane were tuned with pH. The oil/water emulsions at pH 9-10 were converted to middle phase emulsions at pH 6-7 and water/oil emulsions as the pH was further lowered. The magnetization per gram of Fe is similar for the nanoclusters and the primary particles, indicating the spacing between the particles is sufficient to avoid magnetic coupling. The larger volume of nanoclusters relative to the individual primary particles is beneficial for magnetomotive sensing applications including imaging of oil reservoirs, as it increases the force on the particles for a given magnetic field.

Stabilization of superparamagnetic iron oxide nanoclusters in concentrated brine with cross-linked polymer shells.

Iron oxide nanoparticles, in the form of sub-100-nm clusters, were synthesized in the presence of poly(acrylic acid) (PAA) or poly(styrene sulfonate-alt-maleic acid) (PSS-alt-MA) to provide electrosteric stabilization. The superparamagnetic nanoclusters were characterized using a superconducting quantum interference device (SQUID), transmission electron microscopy (TEM), dynamic light scattering (DLS), thermogravimetric analysis (TGA), and zeta potential measurements. To anchor the polymer shell on the nanoparticle surface, the polymer was cross-linked for a range of cross-linking densities. For nanoclusters with only 12% (w/w) PSS-alt-MA, electrosteric stabilization was sufficient even in 8 wt % NaCl. For PAA, the cross-linked polymer shell was essentially permanent and did not desorb even upon dilution of the nanoparticles for iron oxide concentrations down to 0.014 wt %. Without cross-linking, over half of the polymer desorbed from the particle surfaces. This general approach of the adsorption of polymer stabilizers onto nanoparticles followed by cross-linking may be utilized for a wide variety of cross-linkable polymers without the need to form covalent bonds between the nanoparticles and polymer stabilizer. Thus, this cross-linking approach is an efficient and inexpensive method of stabilizing nanoparticles for large-scale applications, including the electromagnetic imaging of subsurface reservoirs, even at high salinity.

Graphene oxide nanoplatelet dispersions in concentrated NaCl and stabilization of oil/water emulsions

Stable dispersions of graphene oxide nanoplatelets were formed in water at pH 2-10 even with 5 wt% NaCl. For these conditions, oil-in-water emulsions stabilized with graphene oxide nanoplatelets remained partially stable for 1 year. The droplet sizes were as small as ~1 μm with a low nanoplatelet concentration of 0.2 wt%. The emulsions were stable even for nanoplatelet concentrations down to 0.001 wt%. The stabilities of the emulsions even at high salinity may be attributed to the high anion density at the graphene oxide nanoplatelet edges which protrude into the water phase. Furthermore, the graphene oxide nanoplatelets are shown to adsorb on the surfaces of the oil droplets. The conceptual picture of graphene oxide nanoplatelets adsorbed to a greater extent on the water side of the oil/water interface, along with the high density of anions on their edges, cause the oil/water interface to curve about the oil phase, resulting in oil-in-water emulsion droplets. The dispersion stability with a very small amount of graphene oxide-based stabilizer, offers an intriguing opportunity for applications including CO2 sequestration and enhanced oil recovery in deep subsurface formations, which generally contain high-salinity brines.

Stabilization of Iron Oxide Nanoparticles in High Sodium and Calcium Brine at High Temperatures with Adsorbed Sulfonated Copolymers

A series of sulfonated random and block copolymers were adsorbed on the surface of ~100 nm iron oxide (IO) nanoparticles (NPs) to provide colloidal stability in extremely concentrated brine composed of 8% wt NaCl + 2% wt CaCl2 (API brine; 1.4 M NaCl + 0.2 M CaCl2) at 90 °C. A combinatorial materials chemistry approach, which employed Ca(2+)-mediated adsorption of anionic acrylic acid-containing sulfonated polymers to preformed citrate-stabilized IO nanoclusters, enabled the investigation of a large number of polymer coatings. Initially a series of poly(2-methyl-2-acrylamidopropanesulfonate-co-acrylic acid) (poly(AMPS-co-AA)) (1:8 to 1:1 mol:mol), poly(styrenesulfonate-block-acrylic acid) (2.4:1 mol:mol), and poly(styrenesulfonate-alt-maleic acid) (3:1 mol:mol) copolymers were screened for solubility in API brine at 90 °C. The ratio of AMPS to AA groups was varied to balance the requirement of colloid dispersibility at high salinity (provided by AMPS) against the need for anchoring of the polymers to the iron oxide surface (via the AA). Steric stabilization of IO NPs coated with poly(AMPS-co-AA) (1:1 mol:mol) provided colloidal stability in API brine at room temperature and 90 °C for up to 1 month. The particles were characterized before and after coating at ambient and elevated temperatures by a variety of techniques including colloidal stability experiments, dynamic light scattering, zeta potential, and thermogravimetric analysis.

pH-Sensitive Polymers for Novel Conformance-Control and Polymer-Flood Applications

Polymer flooding is a commercially proven technology to enhance oil recovery from mature reservoirs. The main mechanism for improving oil recovery is to increase the viscosity of injection water by adding polymer, thereby creating a favorable mobility ratio for improved volumetric sweep efficiency. However, polymer injection brings on several potential problems: a) a high injection pressure with associated pumping cost; b) creation of unwanted injection well fractures; and c) mechanical degradation of polymers due to high shear near wellbore. The high viscosity of polymer solutions and permeability reduction by polymer retention reduce mobility, and simultaneously increase the pressure drop required for the propagation of the polymer bank. The objective of this dissertation is to develop an improved polymer injection process that can minimize the impact of those potential problems in the polymer flooding process, and to extend this application to conformance control. This objective is accomplished by utilizing the pH sensitivity of partially hydrolyzed polyacrylamide (HPAM), which is the most commonly used EOR polymer. The idea of the “low-pH polymer process” is to inject HPAM solution at low-pH conditions into the reservoir. The polymer viscosity is low in that condition, which enables the polymer solution to pass through the near wellbore region with a relatively low pressure drop. This process can save a considerable amount of pump horse power required during injection, and also enables the use of large-molecular-weight polymers without danger of mechanical degradation while injecting below the fracture gradient. Away from the near wellbore region, the polymer solution becomes thickened with an increase in pH, which occurs naturally by a spontaneous reaction between the acid solution and rock minerals. The viscosity increase lowers the brine mobility and increases oil displacement efficiency, as intended. Another potential application of the low-pH polymer injection process is conformance control in a highly heterogeneous reservoir. As a secondary recovery method, water flooding can sweep most oil from the high-permeability zones, but not from the low-permeability zones. The polymer solution under low-pH conditions can be placed deep into such high-permeability sands preferentially, because of its low viscosity. It is then viscosified by a pH increase, caused by geochemical reactions with the rock minerals in the reservoir. With the thickened polymer solution in the high permeability sands, the subsequently injected water is diverted to the low permeability zone, so that the bypassed oil trapped in that zone can be efficiently recovered. To evaluate the low-pH polymer process, extensive laboratory experiments were systematically conducted. As the first step, the rheological properties of HPAM solutions, such as steady-shear viscosity and viscoelastic behavior, were measured as functions of pH. The effects of various process variables, such as polymer concentrations, salinity, polymer molecular weight, and degree…

Effects of Magnetic Field on the Motion of Multiphase Fluids Containing Paramagnetic Nanoparticles in Porous Media

When paramagnetic nanoparticles are adsorbed at the oil-water interface or dispersed in one of the fluid phases in reservoir rock pores, then exposed to an external magnetic field, the resultant particle movements displace the interface. Interfacial tension acts as a restoring force, leading to interfacial fluctuation and a pressure (sound) wave. Here we focus on the interface motion. We apply the theory of ferrofluids to the case of an interface in a cylindrical pore. The predictions are consistent with experiments with an aqueous suspension of iron oxide nanorods in which the interface motion is measured by optical coherence tomography. The relative densities of the fluid phases (air/aqueous and dodecane/aqueous in our case) strongly affect the displacement of the interface. Application of a magnetic field introduces pressure-like terms into the equation of fluid phase motion. We then recast the problem in terms of interface motion, extending a numerical interface-tracking model based on the level-set method to account for capillarity and magnetic pressures simultaneously. We use the model to illustrate the motion of an interface between inviscid fluids at the pore scale when magnetic forces are imposed on one fluid phase.

Measuring and modeling the magnetic settling of superparamagnetic nanoparticle dispersions.

In this paper, we present settling experiments and mathematical modeling to study the magnetic separation of superparamagnetic iron-oxide nanoparticles (SPIONs) from a brine. The experiments were performed using SPIONs suspensions of concentration between 3 and 202g/L dispersed in water and separated from the liquid under the effect of a permanent magnet. A 1D model was developed in the framework of the sedimentation theory with a conservation law for SPIONs and a mass flux function based on the Newtons law for motion in a magnetic field. The model describes both the hindering effect of suspension concentration (n) during settling due to particle collisions and the increase in settling rate due to the attraction of the SPIONs towards the magnet. The flux function was derived from the settling experiments and the numerical model validated against the analytical solution and the experimental data. Suspensions of SPIONs were of 2.8cm initial height, placed on a magnet, and monitored continuously with a digital camera. Applying a magnetic field of 0.5T of polarization, the SPIONs velocity was of approximately 3·10(-5)m/s close to the magnet and decreases of two orders of magnitude across the domain. The process was characterized initially by a classical sedimentation behavior, i.e., an upper interface between the clear water and the suspension slowly moving towards the magnet and a lower interface between the sediment layer and the suspension moving away from the magnet. Subsequently, a rapid separation of nanoparticle occured suggesting a non-classical settling phenomenon induced by magnetic forces which favor particle aggregation and therefore faster settling. The rate of settling decreased with n and an optimal condition for fast separation was found for an initial n of 120g/L. The model agrees well with the measurements in the early stage of the settling, but it fails to describe the upper interface movement during the later stage, probably because of particle aggregation induced by magnetization which is not accounted for in the model.